Cores+threads.... conflicting sources

I understood that CPU usage is limited to threads only. I recently read a post that the metric is actually (cores+threads)/the number yiu wish to use on a plot.
I am curreny using 8 threads on a 64 core 128 thread processor. So which formula is correct
A. (64+128)/8 = 24
B. 128/8 = 16
I know only the first phase uses 8 threads, so the number would only be if every plot used all 8 for all the phases.
I am currently using the second formula which limits my total concurrent to 40 at one time with the limit of 12 in the first phase leaving 4 cores for the computer to run. However, if it is truly cores+threads…
Secondly, how many cores does the computer need to run if I have hit 124 cores in use on plotting out of 128?
Thirdly, even though I am at 124 cores, my cpu usage is always below 40%, why?
Lastly, should one use more ram when using 8 threads instead of 4 on a single plot?
Thanks fellas. Love this community.

The real formula is

Number of Phase 1 plots x threads per plot + number of plots in other phases

Its also possible to assign more threads that you have.
Sometimes this helps, sometimes it causes issues

So I will throw a curveball
Ryzen 5 3600 6C 12 T
Each job gets 12 threads
I run 6 in a stagger on 75mins
I get about 18 - 20 Plots in a rolling 24 hour period.

yes I’ve seen better results as well with overbooking the threads
But I didn’t try anything that radical yet, will give that a try for sure

Interesting. I’ve always wondered about more threads, and why not a lot. After all, task mgr says their are 5730 threads running on my 3600 right now, so what’s a few more chia threads amongst so many friends?